Nuclear reactor and means for inserting neutron-absorbing liquid into the core

ABSTRACT

Installations for mounting, controlling, and guiding control rods in and outside a vessel may be removed and passage through an upper internal part may thereby be avoided. An upper internal part is placed near the core of a reactor and laterally emerges on the outside of the vessel. All the transmission, control, and fluid systems pass through this internal part and emerge, by a mobile connection part, for each cluster of control rods, on an assembly head containing tanks of liquid neutron absorber, and injection circuits in injection channels placed between the fuel rods.

FIELD OF THE INVENTION

The invention relates to nuclear reactors, and in particular to meansfor inserting a neutron absorber, such as a neutron-absorbing liquid,when the latter is used, for controlling and modulating theinstantaneous power of a nuclear reactor. More specifically, with it, itis possible to ensure emergency stopping of the latter, to modulate theflux of neutrons applied for modulating the nuclear power without anysignificant deformation of the core, to regenerate the operating nuclearfuel, and then to use this regenerated fuel without unloading thelatter.

The invention is applied to all types of nuclear reactors, whether theyare reactors with pressurized water, with boiling water, with gascoolant, with molten metals, or even with heavy water.

PRIOR ART AND THE POSED PROBLEM

FIG. 1 shows in a vertical sectional view, a first type of nuclearreactor of the pressurized water type from the prior art. Reference 1designates, as in the other figures, the vessel of the reactor, whilereference 2 designates the fuel rods which form the assembly called thecore 50.

It is noted that an internal part for holding the core called, in thesubsequent patent application, an internal part or internal assemblyreferenced 10A. It is placed above the core 50 containing the fuel 2 andholds the latter into place, in the lower portion of the vessel 1, sothat the latter does not move upwards under the effect of a very largewater flux passing through the core in an ascending movement. So thisinternal part or internal assembly 10 has a mechanical function.

FIG. 3 shows a boiling water type reactor according to the prior art.There again, the core 50 comprising the fuel 2 is placed below theinternal part 10A inside the vessel 1. On the other hand, vapor dryers36 are placed above the internal part 10A.

It is noted that in the reactors from the prior art, the internal part10A or the internal assembly are not in contact with the outside of thevessel 2.

Stiff control rods 51 which are actuated from the outside of the vessel2, are used in both of these nuclear reactor types, as in other types.In the case of the pressurized water reactor illustrated in FIG. 1, thecontrol rods 51 pass through the vessel 2 through the upper lid and passthrough the internal part 10A. Their control and guiding systems clutterup, inter alia, the upper portion of the lid of the vessel 1. In thecase of the boiling water reactor illustrated in FIG. 3, the controlrods 51 penetrate into the vessel through its base and their guiding andcontrol systems are placed under the latter.

As a complement, in pressurized type reactors, it is also common to usea neutron absorber, i.e., boric acid, dissolved in the coolant flux inorder to vary the reactivity homogeneously. On the other hand, varyingthe speed of the pumps is used for varying the reactivity in the boilingwater type nuclear reactors to a lesser extent.

So it is seen that the installation required for controlling andregulating operation of the reactor's core requires a large volume byvirtue of the use of control rods, either above or below the core andpassing through the vessel, and mobilizes cumbersome chemical ormechanical complementary means.

A main object of the invention is therefore to find a remedy to thisdrawback by proposing a different method for controlling the nuclearreaction inside the vessel of the reactor.

SUMMARY OF THE INVENTION

For this purpose, the main object of the invention is a nuclear reactorcomprising:

a vessel;

a core placed in the vessel and containing assemblies of fuel pencils;

at least one internal part placed into the core inside the vessel;

means for inserting a neutron-absorbing liquid inside the assemblies offuel pencils.

According to the invention, said at least one internal part emerges ontothe outside of the vessel in order to connect control devices externalto the vessel of the reactor, to the insertion means placed inside thevessel. Preferably, it emerges laterally, but it may emerge elsewhere onthe vessel of the reactor. The insertion means comprise transmissioncomponents, partly placed in conduits provided in the internal part andemerging on the outside of the vessel on the one hand, and connected tothe means for inserting neutron-absorbing liquid on the other hand.

Preferably, said at least one internal part, is placed above the coreand emerges on the outside of the vessel, laterally.

According to a preferential embodiment of the invention, these means forinserting a neutron-absorbing liquid are means for injecting anddistributing a neutron-absorbing liquid into injection channels placedinside the assemblies of fuel pencils.

Provision is made for placing a helium tank belonging to thetransmission means, in said at least one internal part.

In a first embodiment of the invention, said at least one internal partis located above the core and formed by an upper internal part emergingon the outside of the vessel, of a lower internal part placed below it,inside the vessel.

In a second embodiment of the invention, the internal part is formedwith a single part laterally emerging on the outside.

In order to advantageously complete this arrangement, the nuclearreactor according to the invention is completed with at least oneconnection arm connected to a side connection outlet of said at leastone internal part with the external control devices, the connection armbeing jointed in order to be able to assume two positions which are:

a stretched-out connection position in which a first end of theconnection arm ends outside a pool in which the reactor is emerged, and

a folded position in which the arm is inside said at least one internalpart, transmission components being inside the connection arm. Withthis, the tubes and other cables forming the transmission componentsfound inside the arm, may not have any connection between said at leastone internal part and the outside of the pool.

In the preferential embodiment of the circuit for injecting theneutron-absorbing liquid, the latter comprises at least oneneutron-absorbing liquid tank placed in or beneath the internal part.

Further, it is advantageous to use an assembly head providing theconnection between said at least one internal part and the channels forinjecting the neutron-absorbing liquid, placed below the internal part,an upper portion penetrating or possibly passing through the internalpart.

Conduits of neutron-absorbing liquid each terminated by a swan-neckpenetrate into the tanks and advantageously complete the assembly head.

For the purpose of achieving connections between the conduits placed inthe internal part and the means for injecting the neutron-absorbingliquid, a mobile connection part is advantageously used, placed abovethe internal part, the conduits of the internal part also emerging onthe top of the internal part, the mobile connection part comprising aspace opening above the conduits of the internal part, and the conduitsare used for connecting the conduits of the internal part with the tanksof the neutron-absorbing liquid of the injection means controlled bycontrol means placed outside the vessel.

In this case, it is advantageous to use a mobile bell placed in themobile connection part, above the location where the conduits of theinternal part emerge, and completed with seal gaskets, allowing thedifferent assemblies in the reactor to be connected with a perfect seal.

Several embodiments of the injection channels are possible. Indeed, afirst embodiment consists in using for each of them, an external tubeinside which at least one capillary tube is placed.

For the purpose of compensating particular effects of the reactivity ofthe reactor according to the height in the core, the external tube mayadvantageously have a variable section over the height of the latter,preferably in the height of the external tube.

By placing several capillary tubes in parallel, very fast injection ofthe neutron absorber is obtained. With this particular arrangement, itis possible to achieve an emergency stop system compatible with therequirements for a nuclear reactor.

Another embodiment consists in completing this assembly with the bell,the purpose of which is to vary the neutron spectrum. This bell may bepositioned around an external tube and its capillary tubes.Advantageously, with this last embodiment, it is possible to achieve avariation of the neutron spectrum in the core of the reactor by fillingand emptying at will, this open bell on the fluid of the reactor bymeans of gas transported by the conduits of the internals. By varyingthe neutron spectrum it is also possible to change nuclei of certainirradiated radioactive materials, such as long-lived waste in order tomake them more usable and more storable.

As regards the air distribution circuit, as loading a reactor isperformed under water, the mobile connection part is completed with lidsat the base of the mobile bell to achieve the seal of this part beforeconnection with the conduits of the internal part, the conduits of theassembly head and a conduit of the connection mobile part.

The lids are perforated when the mobile connection part is clamped onthe assembly head.

In the preferential embodiment of the invention, the ducts for injectingand distributing the neutron absorber between the tanks and theinjection channels located in the assemblies of fuels are placed in theassembly head, over several respective stages depending on the type offunction which should be achieved by injecting the neutron absorber intothe selected channels.

As for the electrical distribution circuit, in order to be sealed beforeconnecting it onto the internal part, the mobile connection part iscompleted with lids at the basis of the mobile bell in which a slightlymobile connection part, sealably mounted by means of a gasket, is placedand which may receive a ball valve terminating a cable of the internalpart ending up in the space of the mobile connection part.

An underwater connectible system of electrical or optical connectionsable to operate in a liquid medium under very high pressure is thenachieved.

In an alternative according to the invention, the conduits in theinternal part may be connected to pistons maneuvering stiff controlrods.

In another alternative according to the invention, this internal partmay be fitted out with electrical conductors in order to maneuverelectromagnetic or electric devices which are there also connected tostiff control rods.

The mobile connection parts may lock themselves with their complementaryshapes.

Finally, their water holes may have a partly helical profile in order toset the fluid of the reactor into rotation to homogenize the temperatureof the exiting fluid.

LIST OF FIGURES

The invention and its different technical features will be betterunderstood upon reading the following description, followed by severalfigures respectively illustrating:

FIG. 1, in a front sectional view, a pressurized water nuclear reactoraccording to the prior art;

FIG. 2, in a front sectional view, a pressurized water reactor accordingto the invention;

FIG. 3, in a front sectional view, a boiling water reactor according tothe prior art;

FIG. 4, in a front sectional view, a boiling water reactor according tothe invention;

FIGS. 5A and 5B, theoretical diagrams of nuclear reactor facilitiesaccording to the invention;

FIG. 6A, a top view of the mobile connection part, according to theinvention;

FIG. 6B, a sectional view along line 6B-6B of FIG. 6A;

FIG. 6C, a front sectional view along line 6C-6C of FIG. 6A;

FIG. 7A, a top view of a second embodiment of the mobile connectionpart, according to the invention;

FIG. 7B, a sectional view along line 7B-7B of FIG. 7A;

FIG. 8, as a front sectional view, a first embodiment of an injectionchannel;

FIG. 9, as a front sectional view, a second embodiment of an injectionchannel of the reactor according to the invention;

FIGS. 9A, 9B, 9C and 9D, two shapes used in the second embodiment of theinjection channel according to the invention of FIG. 9;

FIG. 10A, as a sectional view, a third embodiment of an injectionchannel according to the present invention;

FIG. 10B, an application of the embodiments illustrated in FIGS. 8, 9and 10A;

FIG. 11, as a sectional view, a detail of the embodiment of the mobileconnection part of the reactor according to invention;

FIG. 12, as a sectional view, another detail of the embodiment of themobile connection part of the reactor according to the invention;

FIG. 13, a particular shape of the mobile connection parts;

FIG. 14, as a front sectional view, an alternative embodiment of thereactor according to the invention; and

FIG. 15, a complement of the reactor according to the invention.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS OF THE INVENTION

FIG. 5A is a block diagram of the operation of the reactor according tothe invention in the case when the means for inserting a neutronabsorber are means for injecting and distributing a neutron-absorbingliquid, and applied to the assembly of fuel pencils.

A nuclear reactor vessel 1 containing a core 50 itself comprising alarge series of fuel rods 2, is illustrated schematically. Control ofthe reactivity in the core 50 is obtained with a neutron-absorbingliquid injected into channels 7 permanently positioned between the fuelpencils 2 by injection channels 7. Above the core 50, one or more tanksof neutron-absorbing liquid 4 are found from which emerge injectionchannels 7. The whole is placed under the internal part 10 (or theinternal assembly if it is made in several portions) which is used ineach nuclear reactor to hold the core 50 into place, i.e., in the lowerportion of the vessel 1.

This FIG. 5A highlights a portion of the transmission means, i.e., thegas supply and more particularly the helium supply system, allowing theneutron-absorbing liquid to be displaced. Indeed, at least one heliumtank 5 (shown here on the outside) is found in the internal part 10 orits equivalent. Its filling and emptying is controlled by a distributionsolenoid valve 8 completed with a pressure loss diaphragm 6. A returnconduit 7R from the base of each injection channel 7 and ending upstreamfrom the diaphragm 6, allows with the latter, a pressure difference tobe generated between both branches of the injection channel 7 of theneutron-absorbing liquid. This set-up is completed upstream from adischarge tank 3 controlled by a pressurization solenoid valve 9.

It is noted that the internal part 10 or its equivalent emerges on theoutside of the vessel 1, laterally, and has side connectors 17 at thislevel. It may emerge elsewhere for example onto the bottom of thevessel, with other internal connection parts.

Thus, the different conduits, circuits controlling and feeding the meansfor inserting a neutron absorber, notably the helium supply, may beconnected to this internal part 10 outside the vessel with the controlmeans external to the vessel 1. Thus, all the means for regulating thenuclear power of the reactor pass through this internal part, withoutpassing through the vessel or the vessel lid, as this is exactly thecase for control rods used in nuclear reactors of customary design. Thisalso limits the risk of a leak since the ducts transporting thepneumatic, hydraulic fluids, the electrical or optical conductors areintegrated into the bulk of this part 10.

FIGS. 2 and 4 as a respective comparison with FIGS. 1 and 3, show thechanges, enhancements and potential advantages provided by the deviceaccording to the invention. Indeed, the internal part 10 emerging on theoutside of the vessel provides complete control of the core 50 of thereactor. Thus, the upper space inside the vessel 1 is cleared for thepressurized water reactor of FIG. 2 and the space under the vessel 1 ofthe boiling water reactor of FIG. 3 is also cleared.

Indeed, with reference to FIGS. 6A and 6B, it is seen that the mobileconnection part 11 is placed above the internal part which is made herein two portions: a first upper portion 10S and a second lower portion10I. The first upper portion 10S comprises ducts or conduits 100providing supply of power to the means for inserting a neutron absorber.The second one which is the lower portion 10I, corresponds to thetraditional internal part 10A (FIGS. 1 and 3) both geographically andfunctionally, which is attached onto the vessel 1. It also provides thefunction for housing certain pieces of equipment of the storage means,i.e., neutron-absorbing liquid tanks 4, for example an upper tank 4A anda lower tank 4B.

FIG. 6B, as a sectional view, shows a conduit 100 placed inside theupper internal part 10S. It emerges into a cavity 38A of the mobileconnection part 11, around a connection bell 38. In fact, the mobileconnection part 11 is placed above the internal part 10, 10A, or theequivalent assembly, so that it may be dismantled relatively easily, forits maintenance or for changing gaskets or connection members. It isattached thereon by means of screws 26 and a rotation stop for exampleformed with a foldable washer 27. The mobile connection part 11 itselfhas a conduit 110 joining the interior of the connection bell 38 withthe upper portion of the assembly head 12 itself having conduits 120emerging on the tanks 4A and 4B of neutron-absorbing liquid.

These different conduits 100, 110 and 120, are relative to thedistribution of the gas for pushing the neutron-absorbing liquid intothe core of the reactor. It should be taken into consideration thatother distribution networks are installed in the internal part(s) andthe mobile connection part 11. This same upper internal part 10S is usedfor letting through electrical cables, with the purpose of sending backto the outside world information from sensors or control means locatedwithin the reactor. These may be i.a. electrical or optical networks forcontrol or monitoring, and all the other conduits required for the flowof fluid or for signal transmission components.

FIG. 6A shows a top view of the mobile connection part 11, and notablyof its cavity 38A.

It may be seen that other cavities 38B and 38C have been illustrated inthis FIG. 6A. They correspond to communication spaces between differentconduits providing connection of electrical conductors or hydraulic,pneumatic or other conduits, or relating to other units for controllingor monitoring the core of the reactor.

The lower portion of the assembly head has several stages 13. It is seenthat the upper stage 13S receives at the inlet of a conduit, aneutron-absorbing liquid 121, from a neutron-absorbing liquid tank 4Aplaced in a lower internal portion 10I. Swan-necks 39 are used on theinjection channels 7 for the purpose of preventing untimely injectionsof neutron-absorbing liquid. It is easily understood that, with apneumatic control circuit ending in a neutron-absorbing liquid tank 4A,it is possible to inject into first injection channels 7A emerging intothe upper stage 13S, a certain amount of neutron-absorbing liquidintended for achieving a desired result on the moderation of theoperating power of the core of the reactor;

Thus, by having several stages 13 and 13S available, severalneutron-absorbing liquid supply circuits controlled differently andindependently of each other by different conduits, may be provided. Itis thus possible, by using different circuits to modulate the operatingpower of the core, to proceed with an emergency stop or to act on thegeographical distribution of the fission reaction inside the core(offset), i.e., a vertical axial distribution of the nuclear activitywithin the core. To do this, a device similar to the one described byFIG. 5B is used, in which the diaphragm is removed and the portions 7and 7R are separated. On each of these branches, one then has a valve 8,a tank 3 and a control valve 9 with which the height of the neutronabsorber may be adjusted in the injection channel 7.

The second pressure control line is materialized by a return conduit120R in communication with the second end of the injection channelsthrough a return stage 13R extending through a conduit 110R and a mobilebell 38R of the mobile connection part 11 and a conduit 100R of theinternal part 10S.

A water passage 102 is provided around the neutron-absorbing liquidtanks 4A and 4B. At the same time, vents 101 are provided in the mobileconnection part 11 (see FIG. 6A). The latter ones and the volume ofwater 102 account for the passing of water through these controlcomponents and the internal parts 10S and 10I. Indeed, it should be keptin mind that a very large flux of liquid passes through the core of areactor and it has to pass into the upper portion of the vessel, i.e.,pass through the internal part(s) 10, 101 and 10S.

FIG. 6C illustrates the assembly according to another sectional viewalong line 6C-6C of FIG. 6A. Thus, it is possible to see inter aliavents 101 in the internal part 10 and a conduit 120C ending in the lowerneutron-absorbing liquid tank 4B.

FIGS. 7A and 7B illustrate another embodiment of the components whichhave just been described concurrently with FIGS. 6A and 6B. In thisembodiment, the internal assembly formed by both lower 10I and upper 10Sinternal parts is replaced with a single part 10, the shape of which mayrelate to that of the already existing parts. The connection through aconduit 100, the mobile connection part 11 is similar. The latter isstill placed on the upper surface of the internal part 10 by means ofscrews 26. On the other hand, a central passage 112 allows the water toflow through.

A tank part 4 containing two neutron-absorbing liquid tanks 4A and 4B isfound below the internal part 10. In this embodiment, operation issimilar. In other words, the pressure arrives in the neutron-absorbingliquid tanks 4A and 4B via the conduit 120 of an upper portion of theassembly head 12S. The neutron-absorbing liquid flows down one or morestages 13 of a lower portion 12I of the assembly head by means of anextended swan-neck 39 of the supply conduit 121.

FIG. 7A shows the flow of water through the connection module part 11A,i.e., through the central conduit 112. The screws 26 have also beenillustrated in this figure, as well as the spaces 39B of the mobileconnection part 11A and the beginning of the conduits 120.

With reference to FIG. 8, a first embodiment of the injection channelsis provided for proceeding with emergency stops of the reactor. Therapidity of injecting the neutron-absorbing liquid is thereforepreferential here. To achieve this rapid injection, an external tube 80is used, inside which several capillary tubes 82 are placed; with theremaining space 81, it is possible to cause rapid injection of theneutron-absorbing liquid into this assembly by varying the pressure bymeans of helium which acts on the neutron-absorbing liquid tanks. Upon acommand for urgently stopping the reactor, all the capillary tubes 82,mounted in parallel, are fed with neutron-absorbing liquid which rapidlypenetrates into the whole external tube 80.

FIG. 9 shows a sub-assembly used for proceeding with regulation of thepower of the reactor's core. The external tube 90 only contains a singlecapillary tube 92. This is explained by the non-requirement for rapidlyobtaining a large amount of neutron-absorbing liquid. However, thischannel may be used for functions other than the emergency stop.

With reference to FIGS. 9A, 9B, 9C and 9D, the possibility of giving thereference external tube 90 in FIG. 9 a shape with a variable sectionover its height is of interest. Indeed, in FIG. 9A, the external tube900 has a larger section in its upper portion. FIG. 9B shows that thisshape may be cylindrical, with the capillary tube 92 remainingunchanged. With this, it is possible to accumulate a larger amount ofneutron-absorbing liquid in the upper portion of the functional portionof the reactor's core, in order to influence the reactivity of thelatter in a more significative way.

FIGS. 9C and 9D show a second possible shape of the external tube 901,the section of which constantly varies from a certain height and itassumes a flared shape in its front sectional view. FIG. 9D shows thatthe section may also assume the form of a cross.

It may be noted that other shapes of external tubes may be contemplated.A rolling-up of the tube on itself may have the same advantage.

FIG. 10A shows an assembly intended for moderating the flux at the veryinside of the reactor's core. The assembly of FIG. 8 comprising theexternal tube 80 and the injection channels 82 is completed with aspectrum variation bell 18 surrounding the assembly. When the pressurebell 18 is empty, the neutron spectrum enables the fuel to beregenerated. When the pressure bell 18 is filled with the coolant fluid,an increased moderation of the flux is obtained which allows the fuel ofthe reactor to be consumed. These neutron flux changes inside thereactor may also be used as means for varying the reactivity.

Preferably, the spectrum variation bell 18 consists of a zirconium tubeor of any other material transparent to neutrons. When it is filled witha moderator liquid, for example the water of the reactor, it has thesame moderating power with respect to the neutrons as the water flowingoutside this tube. When it is filled with helium or any other gas orliquid, having only an effect on the neutrons, the spectrum variationbell 18 creates a void effect which does not slow down the neutrons andso the neutrons emitted by the fuel pencils may regenerate a fissileatom, for example plutonium, by bombardment of a fissile nucleus whichmay be uranium, plutonium, thorium, for example.

With FIG. 10B, it may be shown how the different injection channels ofFIGS. 8, 9 and 10A are used, as well as the bell 18 of the latter.Indeed, this horizontal sectional view shows the bundle of the core ofthe reactor. The capillary tubes 82 which are each grouped in the middleof a bell 18, form rapid or emergency stop injection tubes. Actually,they may provide a larger amount of helium within a given time. Thecapillary tubes 92 which are placed in the middle of bundles of fuelrods 2 are provided for controlling the reactivity of the reactor. Bell18 assumes the form of a cross including the ends and the inside of thearms which may have a concave shape to fit the cylindrical shape of thefuel rods 2.

It is reported that, within the scope of production of electricity, thefuel rods are therefore consumed over a determined period. In anothermode of use of a nuclear reactor, modified radioactive material rods maybe placed, such as used fuels (having in mind americium, neptunium, andcurium, in particular). Indeed, such materials may become lessradioactive, following their passage in a nuclear reactor of this type,transmutation of these elements even allowing the destruction of suchlong-lived waste. In another words, a particular use of a nuclearreactor of this type is the incineration of long-lived radioactivewaste.

This type of spectrum variation bell provides the possibility ofcontrolling by the gas pressure in the tubes, the ratio between thevolume occupied by the medium which moderates the neutrons in a constantvessel volume and the volume occupied by the fuel. This ratio is called“the void rate”.

This void effect also acts on the moderation effect and because of thissame moderation effect, it changes the power of the reactor.Consequently, the power of the reactor may also be changed by changingthe void rate within the latter.

Operating the pressure inside the channels may be managed in a binary,i.e. on-off way, or used for compensating the flux deformations called“axial offset”. The principle remains the same, but the level of theneutron-absorbing liquid in the injection channel is controlled by thepressure difference which exists across this injection channel. Each endof the latter is connected to a pressurized sphere. The pressure of eachsphere is controlled by a discharge solenoid valve and a fillingsolenoid valve.

FIG. 11 shows a detail of the embodiment of the mobile connection part11 concerning the connections of the pneumatic circuit. Again, a conduit100 is found, passing through the internal part 10 and emerging into thespace 38B of the connection bell 38. For this purpose, lids 19 are usedwith each being crossed by a ball valve 40 provided with a tip 41. Theconnection bell 38 is fitted out with a lower gasket 21 and a sidegasket 22. To adjust the positioning of the connection bell 38 and itssupport on the high mobile connection part 11, a screw 24 acting on aflexible seal membrane is used, placed above the mobile connection bell38.

An example of an electrical connection at this connection part 11, undera gas so as to be sealed off at a very high pressure, is illustrated inFIG. 12, the sectional view being taken along another diameter of themobile connection part 11.

The mobile connection bell 38 and its space 38B are again found with thedifferent gaskets and accessories which allow it to be held in place. Acable 30A emerges from a conduit 100A of the internal part 10B. Thecable 30A may very well not occupy the whole of this conduit 10A.Indeed, other means for transmitting electrical or optical signals maybe used. It is noted that the ball valve 40 includes a central conduit37 allowing the gas from the outside of the vessel to pass through aninsulating part 31. The ball valve 40 with its tip 41 pierces throughthe lid 19, pressurized gas preventing the coolant fluid of the reactorfrom filling the inside of the mobile connection bell 38 and inparticular, a connection part 34 placed in a piston 29 slidably mountedinside the mobile connection bell 38. The seal may be provided with agasket 28 at its level. For this purpose, a spring 32 presses against anadded lid 33 so as to apply a proper connection contact.

Thus, different conductors, for example 35A, of the first cable 30A, maybe put into contact with conductors 35B placed downstream, inside themobile connection part 11. The flexibility of the gasket 28 at thepiston 29 provides centering of the ball valve 40 in the connecting part34.

With such assemblies, the connection between different electrical oroptical conductors, such as optical fibers, may be performed under gasand away from any fluid. Indeed, with the gasket 28 of the piston 29,the latter may have a slight play so that the ball valve 40 may becentered via a centering part 20.

As shown in FIG. 13, the mobile connection part 11A may have acomplementary shape which allows them to nest in each other, which makesthem self-locking. Further, the water holes 101A may be profiled inorder to set the fluid into rotation, which mixes and homogenizes thetemperature of the water flowing out of the assemblies.

FIG. 14 shows an alternative in which control rods are used.Transmission means 203, which may be electrical cables, but also feedpipes, pass through the internal part(s) 10 c and put the drivingdisplacement means or other means 201 driven with pneumatic, hydraulicor electrical power, into relation with the outside of the vessel, whichmaneuver axes 202 permanently attached to the control rods. In thiscase, the driving displacement means 201 are placed above the internalpart 10 c.

With this system, although less performing, it is also possible toregulate a nuclear reactor without passing through the vessel lid orthrough the vessel itself.

It is noted that in all the variations of the system according to theinvention, it is possible to use the internal part 10 or its equivalent,i.e., parts 10I and 10S, for installing tubes or conduits therein, thefunction of which is to feed pressure bells at will, open onto thecoolant fluid of the reactor and located in or between the fuelassemblies. In this case, by varying the pressure, it is possible tovary the level of the coolant fluid in the pressure bell around theinjection channels.

In all the alternatives according to the invention, the internal parts10, 10S and 10I, may also be used for allowing the passage of anyconductor, the function of which is to transmit signals emitted bymeasuring or viewing means, such as fission chambers or neutrondetectors, for example of the collectron or fission chamber type, formeasuring the neutron flux and determining a flux map, thermocouples,optical fibers and cameras. They are also used for bringing back to theoutside world, information from measuring sensors or monitoring meanslocated in the reactor. A connection is then used such as the oneillustrated by FIG. 12, these cables passing through the insulating part31 and piercing the lid 19.

The internal parts, 10, 10S or 10I, comprising transmission components,are not necessarily placed above the core. It may be contemplated toplace them below the core, for example.

With reference to FIG. 15, the conduits 100 laterally placed in theinternal part(s) 10 end in a side outlet 217. Advantageously, they maybe extended by identical cables or conduits 152 which are borne by ajointed arm 300. Indeed, the latter may be attached to the end of theinternal part 10 through a base 153. Each jointed arm has severalsections which may be laid out in order to reach the edge of the pool150 in which the reactor is installed. This laid-out position isillustrated by the sections 151A. Thus, all the tubes required forpressurizing each of the tanks containing neutron-absorbing liquid, maybe “without any connection”, from the edge of the pool where controldevices are found, to the interior of the internal part. The sideconnectors 17 of the embodiment illustrated in FIGS. 5A and 5B, are thensuppressed.

In other words, the conduit 100 in the preferred application accordingto the invention may be a continuous tube from the interior of theinternal part 10 of the reactor up to the end of the arm 300 of thereactor. Connection to the other apparatuses forms the basic schemerequired for operating the reactor.

Another possibility consists in connecting a tube or flexible tube tothe outlet of the upper internal part 10S by a weld, a connector, oranother component. On the other side, this same tube or flexible tubemay be connected to one of the tubes contained in the sections 151A ofthe arm 300, and this in an identical way (weld, or other connection).However, this last method adds one connection per tube, it is thereforeless reliable.

With the joint of the jointed arm, the latter may be folded as indicatedby the position of the sections 151B. Indeed, the latter are again foundinside the internal part 10. The use of this position is provided forthe case of unloading the fuel inside the core 50 of the nuclear reactorfor which the internal part 10 needs to be removed. The latter maythereby be removed and laid down outside the pool with reduced bulk, thejointed arm being inside the latter.

Thus, once it is stretched out, the jointed arm allows the electrical,pneumatic or other connection points to be transferred outside the pool.The joint may be obtained by welding flexes, which may be in stainlesssteel, to the joints, or by using the so-called “pig tail” or “flexibleloop”, i.e., a loop on a pipe allowing it to deform.

Thus, it is possible to stretch out more than 10 m of jointed arm (theheight of water in the pool) above the internal part.

The jointed arm(s) may be maneuvered by means of electrical motors orcylinders.

ADVANTAGES OF THE INVENTION

The invention suppresses all the bushings of the lid of the vessel andthe bushings of the bottom of the vessel or of the lid of the vessel,which are absolutely necessary in a conventional nuclear reactor forproviding all the connection, measuring, monitoring and controlfunctions inside the reactor.

The internal part(s) described in this document may be parts added tothe initially provided internal part in the vessel.

In any case, the internal part of the device according to the inventionmay very well provide the mechanical function preventing the core of thereactor and the fuel from being lifted by the flux of coolant fluid.

The invention may be applied to all types of reactor, whether they arereactors with pressurized water, with boiling water, with gas coolant,with molten metal, or even with heavy water. The use of control rods tobe inserted between the fuel rods and of all the guiding devices of thelatter found above the core and outside the vessel, may thereby besuppressed.

The channels may thereby be filled and emptied with several types ofneutron-absorbing liquids, such as metals or metal alloys, optionallyadded with neutron-absorbing solid particles of the same density as themetal or the alloy. The neutron-absorbing liquids remain liquid at allthe operating temperatures of a nuclear reactor, including those underaccidental temperature conditions.

The subassembly of the device consisting inter alia of the assemblyhead, the neutron-absorbing liquid tanks and the injection channels,being provided at the same time as the fuel assemblies and below theoperating temperature of the reactor, the injection channels are filledwith the neutron-absorbing mixture which is now solid. This provides aconsiderable advantage, notably during the fuel transport and handlingphases. This provides the device with a further safety level.

By positioning the helium tank inside the upper internal part, thelatter may be made stable in temperature and forms a passive systementirely in the reactor. Indeed, injection of neutron absorber isperformed in the case of failure of the piping external to the vessel.

The bell used for varying the spectrum may vary the neutron spectrum,which allows the fuel to be regenerated. When it is filled with thecoolant fluid, an increased moderation of the flux is achieved whichallows the fuel of the reactor, which has been regenerated, to beconsumed, and thus extends the cycle of the fuel.

Other advantages relate to the loading of the core of the reactorprovided with the control device according to the invention.

Indeed, once the fuel has been put inside the vessel of the reactor, theinternal part 10A or 10B or the equivalent assembly is laid over thelatter. The mobile connection part 11 is then placed, the connectorsconnected to the outside being also connected to a pressurized gassupply, thereby preventing the passage of water. Indeed, as the mobileconnection part 11 is removable and provided with lids 19, water cannottherefore penetrate into this mobile connection part 11.

By tightening the mobile connection part 11 onto the internal part 10,10S and optionally onto the upper portion 12S of the assembly head, thetip 4 i of the ball valve 40 may pierce the lid 19 and be driven intothe latter.

By tightening the screw 14, it is possible to obtain a perfect seal onthe internal part 10 or 10S. The bell 38 is put into communication withthe tubes and conduits in the mobile connection part 11. Thus, theconnection between the gas supply and the tanks 4A and 4B ofneutron-absorbing liquid and the injection channels 7 is safelyachieved, without having introduced any water into the circuit. Such aconnection may moreover be monitored by measuring the gas leaksidentified in the reactor. In the case of poor tightening, the operationmay be resumed, the mobile connection part 11 changed, without having toremove internal parts used for supporting the fuel and the core of thereactor. This is an availability and safety advantage for upkeeping andmaintaining the nuclear reactor.

It is possible to intervene on one or more control devices relative toone or more fuel assemblies.

On the other hand, the invention provides four different controlfunctions in the operation of the reactors, which are:

stopping the reactor in an emergency with high speed for inserting theneutron-absorbing liquid;

monitoring the power of the operating reactor;

correcting flux deformations inside the core;

changing the neutron spectrum inside the core.

It is noted that the emergency stop is of the passive type.

With the invention it is also possible to dissociate the coolant fluidfrom the materials which are used for controlling the reactor. One thusgets rid of the chemical handling of the coolant fluid and of thedrawbacks resulting from the presence of boric acid in the coolantcircuits (corrosion).

Of course, any repair on the mobile connection part 11 is possible,assembling by assembling the fuel, without having to remove the partsused for holding the fuel in place, i.e., the internal part.

With the invention, it is possible to multiply the number of controldevices, without requiring a large number of passages through the wallof the vault of the reactor or the internal parts. With thismultiplicity of control components it is possible to reduce dissymmetryof the neutron flux in an operating reactor.

By using the diaphragm 6 on the pneumatic circuit, the use of twocircuits may be suppressed by generating a differential pressure betweenboth branches of the tube 7.

By using one or more jointed arms, it is possible to transfer theconnection point of the whole set of conduits connecting the core of thereactor to the outside of the pool.

1-24. (canceled)
 25. A nuclear reactor comprising: a vessel; a coreplaced in the vessel and containing assemblies of fuel rods; at leastone internal part place inside the vessel; wherein the at least oneinternal part emerges on the outside of the vessel to provide aconnection between the inside and the outside of the vessel, therebyconnecting external control devices with means for inserting a neutronabsorber, placed inside the vessel, and the means for inserting aneutron absorber comprises transmission components partly placed inconduits provided in the at least one internal part and being connectedto means for inserting a liquid neutron absorber.
 26. The nuclearreactor according to claim 25, wherein the at least one internal part isplaced above the core and emerges on the outside of the vessel,laterally.
 27. The nuclear reactor according to claim 25, furthercomprising at least one connection arm connected to a side connectionoutlet of the at least one internal part and with the external controldevices, the connection arm being jointed to be able to assume twopositions of: a stretched-out connection position, in which a first endof the connection arm is outside the pool, and a folded position, inwhich the connection arm is folded inside the at least one internalpart, transmission components being inside the connection arm.
 28. Thenuclear reactor according to claim 26, further comprising at least oneconnection arm connected to a side connection outlet of the at least oneinternal part and with the external control devices, the connection armbeing jointed to be able to assume two positions of: a stretched-outconnection position, in which a first end of the connection arm isoutside the pool, and a folded position, in which the connection arm isfolded inside the at least one internal part, transmission componentsbeing inside the connection arm.
 29. The nuclear reactor according toclaim 25, wherein the insertion means are formed by means for injectinga liquid neutron absorber into the injection channels placed inside thefuel rod assemblies.
 30. The nuclear reactor according to claim 26,wherein the insertion means are formed by means for injecting a liquidneutron absorber into the injection channels placed inside the fuel rodassemblies.
 31. The nuclear reactor according to claim 27, wherein theinsertion means are formed by means for injecting a liquid neutronabsorber into the injection channels placed inside the fuel rodassemblies.
 32. The nuclear reactor according to claim 28, wherein theinsertion means are formed by means for injecting a liquid neutronabsorber into the injection channels placed inside the fuel rodassemblies.
 33. The nuclear reactor according to claim 25, wherein thetransmission means comprises a helium tank placed in the at least oneinternal part.
 34. The nuclear reactor according to claim 25, whereinthe at least one internal part includes two internal parts of an upperinternal part emerging on the outside and a lower internal part placedunder the upper internal part, inside the vessel.
 35. The nuclearreactor according to claim 25, wherein the at least one internal partcomprises a single internal part emerging on the outside of vessel. 36.The nuclear reactor according to claim 29, wherein the means forinjecting a liquid neutron absorber comprises, for each fuel rodassembly, at least one tank of liquid neutron absorber placed in orabove the at least one internal part.
 37. The nuclear reactor accordingto claim 36, further comprising an assembly head providing connectionbetween the internal part and the channels for injecting the liquidneutron absorber located in the fuel rod assemblies placed below theinternal part, an upper portion optionally penetrating or passingthrough the internal part.
 38. The nuclear reactor according to claim37, wherein a junction of the tanks with the injection channels isachieved by liquid neutron absorber conduits each extended by aswan-neck.
 39. The nuclear reactor according to claim 29, furthercomprising, for each assembly of fuel rods, a mobile connection partplaced above the at least one internal part to provide connectionsbetween the conduits placed in the internal part and means for injectinga liquid neutron absorber, the mobile connection part including a spaceemerging above the conduits of the internal part and further comprisingconduits connecting the conduits of the internal part with the liquidneutron absorber tanks of the injection means controlled by controlmeans placed outside the vessel.
 40. The nuclear reactor according toclaim 39, wherein for each fuel rod assembly, a mobile bell is placed inthe space of the mobile connection part, above the location whereconduits of the internal part emerge, and being completed with seals.41. The nuclear reactor according to claim 39, further comprising, foreach fuel rod assembly, a pneumatic distribution circuit, the mobileconnection part being then completed with lids, at a base of the mobilebells, to provide the seal, before tightening the mobile part oninternals, of the connection between the different conduits of theinternal part, the conduits of the mobile connection part and those ofthe assembly head.
 42. The nuclear reactor according to claim 39,further comprising, for each fuel rod assembly, an electricaldistribution circuit, the mobile connection part being completed withlids at the base of the mobile bell, in which is placed a mobileconnecting part sealably mounted by a joint, and configured to receive aball valve terminating a cable of the internal part ending in the spaceof the mobile connection.
 43. The nuclear reactor according to claim 29,wherein, for each fuel rod assembly, ducts for injecting anddistributing the neutron absorber between the tanks and the injectionchannels are placed in an assembly head on plural respective stagesdepending on the type of injection.
 44. The nuclear reactor according toclaim 29, wherein portions of the injection channels each include anexternal tube, inside which at least one capillary tube is placed. 45.The nuclear reactor according to claim 44, wherein the external tube hasa variable section over the height of the latter.
 46. The nuclearreactor according to claim 45, wherein the variable section is found inthe upper portion of the external tube.
 47. The nuclear reactoraccording to claim 43, wherein a portion of the injection channelscomprise a bell inside which the external tube and the at least onecapillary tube are placed.
 48. The nuclear reactor according to claim44, wherein the injection channels are mounted in parallel.
 49. Thenuclear reactor according to claim 25, further comprising pistonsmaneuvering control rods between the fuel rods and controlled viaconduits of the at least one internal part.
 50. The nuclear reactoraccording to claim 25, further comprising electrical and/orelectromagnetic devices for maneuvering control rods between the fuelrods and controlled via conduits of the at least one internal part. 51.The nuclear reactor according to claim 38, wherein the mobile connectionparts have complementary shapes to self-lock.
 52. The nuclear reactoraccording to claim 38, wherein the mobile connection parts have waterholes with a partly helical profile.